fn start_counter()

in reverie-ptrace/src/validation.rs [193:262]

• 63 lines of code
• 5 McCabe index (conditional complexity)

fn start_counter(
    tid: libc::pid_t,
    group_fd: libc::c_int,
    attr: &mut perf::perf_event_attr,
    mut disabled_txcp: Option<&mut bool>,
) -> Result<ScopedFd, PmuValidationError> {
    attr.set_pinned((group_fd == -1) as u64);

    if let Some(disabled) = disabled_txcp.as_mut() {
        **disabled = false
    }

    let fd_result = Errno::result(unsafe {
        libc::syscall(
            libc::SYS_perf_event_open,
            attr as *mut perf::perf_event_attr,
            tid,
            -1,
            group_fd,
            perf::PERF_FLAG_FD_CLOEXEC,
        )
    });

    match &fd_result {
        Err(Errno::EINVAL) if attr.config & IN_TXCP > 0 => {
            // The kernel might not support IN_TXCP, so try again without it.
            let mut tmp_attr = *attr;
            tmp_attr.config &= !IN_TXCP;

            let no_txcp_fd = Errno::result(unsafe {
                libc::syscall(
                    libc::SYS_perf_event_open,
                    &tmp_attr,
                    tid,
                    -1,
                    group_fd,
                    perf::PERF_FLAG_FD_CLOEXEC,
                )
            });

            if no_txcp_fd.is_ok() {
                if let Some(disabled) = disabled_txcp.as_mut() {
                    **disabled = true
                }
                warn!("kernel does not support IN_TXCP");
            }

            no_txcp_fd
        }
        _ => fd_result,
    }
    .map(|raw_fd| raw_fd.into())
    .map_err(|errno| match errno {
        Errno::EACCES => PmuValidationError::CouldNotCreateTimer {
            errno,
            msg: "Permission denied to use 'perf_event_open'; are hardware perf events \
                available? See https://github.com/rr-debugger/rr/wiki/Will-rr-work-on-my-system",
        },
        Errno::ENOENT => PmuValidationError::CouldNotCreateTimer {
            errno,
            msg: "Unable to open performance counter with 'perf_event_open'; \
                are hardware perf events available? See \
                https://github.com/rr-debugger/rr/wiki/Will-rr-work-on-my-system",
        },
        _ => PmuValidationError::CouldNotCreateTimer {
            errno,
            msg: "See - https://man7.org/linux/man-pages/man3/errno.3.html",
        },
    })
}